The goal of this proposal is to take advantage of the highly conserved 3' noncoding region (NTR) of the hepatitis C virus (HCV) genome to develop an assay to measure HCV RNA in serum of HCV-infected patients. HCV is the most prevalent chronic bloodborne infection in the U.S. Although the number of new infections has declined substantially, there are still an estimated 36,000 new infections each year and approximately 1.8 percent of the U.S. population (3.9 million) is chronically infected. As much as 40 percent of chronic liver disease is HCV related and this results in up to 10,000 deaths each year. The presence of anti-HCV antibody does not distinguish between acute, chronic, or resolved infection nor can anti-HCV antibody levels be used to monitor disease progression or therapeutic efficacy. Qualitative HCV RNA detection assays have been helpful in establishing the diagnosis of HCV in many cases and quantitative measurement of HCV RNA levels in serum has been successfully used to predict response to therapy. Several qualitative and quantitative HCV RNA assays have been developed, but none is without technical problems and none has yet received FDA approval. Optimal management of HCV infections and further progress toward understanding HCV pathogenesis will depend on ongoing efforts to maximize the performance of HCV RNA load assays. This proposal targets a unique region of the genome which may be critical to achieving this goal. PROPOSED COMMERCIAL APPLICATION Measurement of the level of HCV RNA in serum is becoming an increasingly important component of the management of patients who are chronically infected with HCV. Optimal management of HCV infections will depend on continued efforts to maximize the performance of HCV RNA load assays. If the 3'NTR proves to be the optimal genomic target for measuring HCV RNA, the work proposed here will be directly applied to a commercially and clinically valuable HCV viral load test.